How to finish the roof side of parapet walls
Find out why it’s essential to use roof coverboard instead of exterior wall sheathing
When it comes to the construction and long-term durability of commercial roofing systems, every detail matters, including the choice of materials for the roof side of parapet walls.
A parapet wall is a low, protective barrier that extends vertically along the edge of a roof. It is primarily designed for safety to help prevent falls, but can also serve aesthetic purposes and hide roof equipment such as air-conditioning units.
For commercial building construction, after the wall sheathing is installed, there is often a time gap between the completion of the parapet wall and the roof installation. That leaves many exterior wall contractors asking how the roof side of the parapet should be finished so it is protected from the weather during this window of time.
This article provides guidance on using roof coverboard for the roof side of parapets for two critical reasons:
- Weather protection
- Compatibility with the roof system warrant
Is the roof side of the parapet part of the exterior wall or part of the roof?
One of the most common mistakes when finishing the roof side of a parapet wall is using exterior wall sheathing. The back or roof side of the parapet is considered part of the roof assembly — the roof membrane extends up the back side of the parapet — and exterior wall sheathing isn’t designed to be used in UL roof assemblies.
In this scenario, fiberglass-faced roof boards such as DEXcell FA® Glass Mat Roof Board are recommended for use on the roof side of the parapet to protect it from weather during the period between completion of the parapet and roof installation. Manufactured by Gold Bond Building Products, an affiliate of National Gypsum Company, DEXcell FA Glass Mat Roof Board comes with a 90-day exposure warranty, which allows ample time for the transition from exterior wall construction to roof installation.
In addition, DEXcell FA Glass Mat Roof Board is approved for use in UL fire-rated roof assemblies, whereas exterior wall sheathing is not.
DEXcell FA Glass Mat Roof Board benefits include:
- UL roof assemblies: Available in a 5/8" thickness that is UL Classified for use in fire-rated assemblies, including UL “P” roof assemblies
- Fire ratings: Meets F#asset:266933:transform:cardMediaTopM Class 1 and UL Class A fire ratings for roofing systems of any slope per UL 790/ULV S107
- Thermal barrier: Provides a heat sink barrier to improve the overall life span of the roof membrane
- Mold and moisture resistant: Scores a 10, the best possible score on A#asset:266933:urlSTM D3273,Standard Test Method for Resistance to Growth of Mold on the Surface of Interior Coatings in an Environmental Chamber
If exterior wall sheathing has been installed on the roof side of a parapet, roof boards can be installed over the sheathing to comply with the roofing assembly specifications. Of course, always follow the roof system manufacturer’s application recommendations.
What is the purpose of a parapet wall?
As noted earlier, parapet walls serve both aesthetic and functional needs for buildings.
- Aesthetics: Parapets add height and provide space for decorative details.
- Safety: Parapets provide fall protection for maintenance crews working on the roof.
- Wind protection: Parapets create a windbreak to lessen force on the roof.
- Conceal rooftop mechanicals: Commercial and multifamily residential roofs often house mechanical systems such as HVAC units, and the parapet wall blocks these systems, providing a clean view of the facade.
The DEXcell® roof coverboard family of products can contribute to a longer roof life.
Choose from DEXcell FA VSH® Glass Mat Roof Board, DEXcell FA® Glass Mat Roof Board and DEXcell® Glass Mat Roof Board to meet the specific needs of your location and fortify roofs in a variety of ways.
- DEXcell roof coverboards provide a stout surface to protect the roof from foot traffic from service technicians, electricians and plumbers doing routine maintenance and repairs.
- DEXcell roof coverboards contribute to higher STC ratings because they include a high-density gypsum core.
- DEXcell FA VSH Glass Mat Roof Board features a stronger core and heavy-duty coated fiberglass facer to protect against hail damage and punctures.
Need technical assistance?
Call our experts at 1-800-NATIONAL® Construction Services for insights into roof assembly performance.
